The life cycle of Northern Hemisphere downward wave coupling between the stratosphere and troposphere

Tiffany Shaw

The life cycle of Northern Hemisphere downward wave coupling between the stratosphere and troposphere via wave reflection is analyzed. Wave reflection events are defined by extreme negative values of a wave-coupling index based on daily wave-1 heat flux in the stratosphere. The life cycle occurs over a 28-day period. The evolution in the stratosphere is consistent with linear theory. Following the evolution in the stratosphere there is a shift toward the positive phase of the North Atlantic Oscillation (NAO) in the troposphere. The results suggest that wave reflection events can directly influence tropospheric weather. In addition, seasons with multiple wave reflection events have a positive NAO phase and are opposite to seasons with major sudden stratospheric warmings which have a negative NAO phase. Finally, general circulation models that do not properly resolve the stratosphere systematically underestimate stratospheric wave reflection and therefore may be missing an amplifying factor of the NAO.